The vacuum forming or deep drawing of synthetic resin or thermoplastic foil webs into mold cavities of respective mold halves, and the use of such mold halves to fuse the container halves thus formed together when the mold halves are pressed toward one another is described, inter alia, in Austrian Pat. No. 284 430.
In the device of this patent, the mold halves are movable back and forth in a horizontal plane located below the extrusion press from which the thermoplastic foil is extruded.
During the article-forming processes and the associated cooling time, the extrusion press must be brought to standstill and the means for carrying off the finished article must likewise be halted. The latter means is again operated once the mold halves are spread apart to release the finished article, whereupon the extrusion press can be restarted to permit a sufficient foil portion to be introduced between the mold halves.
This, naturally, requires intermittent drives for the extrusion press and the means for carrying off the vacuum-formed articles.
Furthermore, there is a tendency when the foil is constituted by a pair of foil webs or strips, for the strips to come together during any standstill of the extrusion press and this, of course, is highly undesirable because the two webs may fuse together and give rise to defects in the products made. Consequently it is desirable to operate to greatest possible extent with a continuous output from the extrusion press, i.e. uninterrupted feed of the material from the latter.
The disadvantage of this approach, of course, is that an accumulation of the extruded foil is found upstream of the mold halves while the latter are closed or operative to form respective container halves for an article. In some cases this accumulation cannot be handled readily and backed up material must be removed before operation is again effective.
Discontinuous withdrawal of the foil from the extruder may result in a backup at the extruder with blockage of the extruder nozzles or thickening of the extruded foil at various locations, also to the detriment of the uniformity and quality of the finished products.